One explaination for the use of fuses might be high short circuit current beyond the interrupting capacity of the circuit breakers. There are systems where circuit breakers for the desired interrupting capacity are not cost effective and fuses are used to protect the circuit.
I would appreciate if someone could discuss the disadvantages of unbalanced loads on delta-delta power transformer. Assuming the loading is within the transformer rating, are there any undesirable consequences of this? Any effect on power system harmonics, delta circulating currents, or whatever...